Use Of Adsorption Isotherms Research Articles

Experimental study of the remediation of acid mine drainage by Maifan stones combined with SRB.

The problems of acid mine drainage (AMD) in coal mine acidic wastewaters arise from a range of sources, including severe pollution with heavy metals and SO42- and difficulties during treatment. Based on the ability of Maifan stone to adsorb heavy metals and the dissimilatory reduction of SO42- by sulfate-reducing bacteria (SRB), Maifan stone-sulfate-reducing bacterium-immobilized particles were prepared via immobilization techniques using Shandong Maifan stone as the experimental material. The effects of Maifan stones containing SRB on mitigating AMD were investigated by constructing Dynamic Column 1 with Maifan stone-sulfate-reducing bacterium-immobilized particles and by constructing Dynamic Column 2 with SRB mixed with Maifan stones. By the use of adsorption isotherms, adsorption kinetics, a reduction kinetics model and X-ray diffraction (XRD) and scanning electron microscopy (SEM) studies, the mechanism by which Maifan stone-sulfate-reducing bacterium-immobilized particles mitigate AMD was revealed. The results showed that the total effect of Maifan stone-sulfate-reducing bacterium-immobilized particles on AMD was better than that of biological Maifan stone carriers. The highest rates for the removal of Fe2+, Mn2+, and SO42- in AMD were 90.51%, 85.75% and 93.61%, respectively, and the pH value of the wastewater increased from 4.08 to 7.64. The isotherms for the adsorption of Fe2+ and Mn2+ on Maifan stone-sulfate-reducing bacterium-immobilized particles conformed to the output of the Langmuir model. The adsorption kinetics were in accordance with Lagergren first-order kinetics, and the kinetics for the reduction of SO42- conformed to those of a first-order reaction model.

Reduction of excessive heavy metals accumulation in drinking water with natural zeolites

This paper reports on the study of heavy metal removal from groundwater intended for human consumption using natural aluminosilicates of the zeolite group. The natural zeolite material has been extracted from the Sokirnica deposit located in the Zakarpattia Region in Ukraine. The central focus of this study was the course of the heavy metal adsorption process itself, in which natural zeolites were applied for the removal of Cr, Cd, Ni and Pb ions from aqueous solutions in the presence of large amounts of Ca and Mg ions, competing for ion exchange sites. The capacity of zeolite as an adsorbent was assessed with the use of adsorption isotherms prepared for the heavy metals under tests, whereas the mathematical description of the process was provided by Freundlich and Langmuir isotherm equations. The results from the analysis confirm the high efficiency, and thus the applicability, of zeolite deposits in water filtration. The effective Cr, Cd, Ni and Pb removal rate from groundwater intended for human consumption was confirmed even when the content of these metals in water was exceeded by a factor of 10, compared to the permissible limits provided in legal regulations.

Numerical Simulation of Gas Production from Gas Shale Reservoirs—Influence of Gas Sorption Hysteresis

The true contribution of gas desorption to shale gas production is often overshadowed by the use of adsorption isotherms for desorbed gas calculations on the assumption that both processes are identical under high pressure, high temperature conditions. In this study, three shale samples were used to study the adsorption and desorption isotherms of methane at a temperature of 80 °C, using volumetric method. The resulting isotherms were modeled using the Langmuir model, following the conversion of measured excess amounts to absolute values. All three samples exhibited significant hysteresis between the sorption processes and the desorption isotherms gave lower Langmuir parameters than the corresponding adsorption isotherms. Langmuir volume showed positive correlation with total organic carbon (TOC) content for both sorption processes. A compositional three-dimensional (3D), dual-porosity model was then developed in GEM® (a product of the Computer Modelling Group (CMG) Ltd., Calgary, AB, Canada) to test the effect of the observed hysteresis on shale gas production. For each sample, a base scenario, corresponding to a “no-sorption” case was compared against two other cases; one with adsorption Langmuir parameters (adsorption case) and the other with desorption Langmuir parameters (desorption case). The simulation results showed that while gas production can be significantly under-predicted if gas sorption is not considered, the use of adsorption isotherms in lieu of desorption can lead to over-prediction of gas production performances.

Application of a new dynamic transport model to predict the evolution of performances throughout the nanofiltration of single salt solutions in concentration and diafiltration modes

Although many knowledge models describing the rejection of ionic compounds by nanofiltration membranes are available in literature, they are all used in full recycling mode. Indeed, both permeate and retentate streams are recycled in order to maintain constant concentrations in the feed solution. However, nanofiltration of real effluents is implemented either in concentration or diafiltration modes, for which the permeate stream is collected. In these conditions, concentrations progressively evolve during filtration and classical models fail to predict performances. In this paper, an improvement of the so called “Donnan Steric Pore Model”, which includes both volume and concentration variations over time is proposed. This dynamic model is used here to predict the evolution of volumes and concentrations in both permeate and retentate streams during the filtration of salt solutions. This model was found to predict accurately the filtration performances with various salts whether the filtration is performed in concentration or diafiltration modes. The parameters of the usual model can be easily assessed from full batch experiments before being used in the dynamic version. Nevertheless, it is also highlighted that the variation of the membrane charge due to the evolution of feed concentration over time has to be taken into account in the model through the use of adsorption isotherms.

Determining water in transformer paper insulation: analyzing aging transformers

It is important to monitor the water concentration in the insulation of aging power transformers, because over time the insulation becomes wet, due to water ingress from the atmosphere and water formed in chemical reactions involving oxygen. If the water concentration is sufficiently high, the insulation will age prematurely [1] and the transformer may fail if overloaded [2]. In a previous article [3] we reported on the measurement of water concentration in the insulation paper of a power transformer that had been in service for only seven years. The waterconcentration data obtained using on-line water-activity probes were compared with corresponding data obtained from dielectric response measurements. In that work cellulose adsorption isotherms were used to process the water-activity-probe data. However, according to [4] and [5], inaccuracies in the waterconcentration estimates may result from the use of adsorption isotherms. According to [6], these inaccuracies may exceed 200%. The probable main causes are the transformer insulation materials not reaching thermal equilibrium, the water concentration within the insulation not being uniform, and variability in the properties of the insulating materials.

Biosorption of heavy metals by Zoogloea ramigera: use of adsorption isotherms and a comparison of biosorption characteristics

The biosorption of lead(II), copper(II), nickel(II), and iron(III) ions on Zoogloea ramigera, an activated sludge bacterium, was studied with respect to adsorption pH and temperature in order to determine the optimum conditions for heavy metal removal. Optimum initial pH for the biosorption of lead(II), nickel(II) and copper(II) ions by Z. ramigera was determined as 4.0–4.5 whereas higher biosorptive uptake of iron(III) ions by Z. ramigera was obtained at pH 2.0. Maximum biosorption rates of nickel(II) and copper(II) ions by Z. ramigera where obtained at 25°C, while the initial biosorption rates and the adsorptive capacity of the biomass for lead(II) and iron(III) ions increased with increasing temperatures in the range 25–45°C. The adsorption isotherms were developed for optimum conditions and it was seen that the adsorption equilibrium data fit both Freundlich and Langmuir isotherms within the metal ion concentrations studied (25–200 mg 1 −1). The adsorption constants for lead(II) and iron(III) were higher than those for nickel(II) and copper(II) for both Langmuir and Freundlich models.

Use of adsorption isotherms of light normal alkanes for characterizing microporous activated carbons

Adsorption isotherms of light normal alkanes on three different activated carbons were measured and compared with benzene adsorption isotherms on these carbons. Analysis by means of the Dubinin-Radushkevich equation revealed the utility of the adsorption isotherms of ethane, propane, and n-butane for describing the microporosity of activated carbons. On the basis of these studies, the authors recommend that n-butane be used as a reference adsorbate for characterization of microporous activated carbons.

Displacement Analysis of Terpene Hydrocarbons:*: I. Preliminary Studies

Displacement analysis on silica gel has been investigated as a method of separating terpene hydrocarbons. The use of adsorption isotherms in predicting the nature of displacement diagrams has been substantiated. An application of displacement analysis to a mixture of terpene hydrocarbons isolated from a natural source is presented.

The Use of Adsorption Isotherms for Measuring the Surface Areas of Catalysts and Other Finely Divided Materials

We systematically study anion exchange membrane fuel cells (AEMFCs) based on poly(aryl-co-aryl piperidinium) (c-PAP) copolymers and provide a scalable scenario for high-performance AEMFCs, covering the optimization of the relative humidity (RH), catalyst species, catalyst interfaces, and hydrophobic treatment. Specifically, high-water-permeable c-PAP ionomers in the presence of moderate relative humidity (RH) (75%/100%) can be used to address anode flooding and cathode dry-out issues. The composition of the catalyst layer and the anode hydrophobic treatment significantly impact the power density of AEMFCs. c-PAP-based AEMFCs with optimum catalyst composition achieve a peak power density (PPD) of 2.70 W cm-2 at 80 oC in H2-O2 after hydrophobic treatment. Pt1Co1/C cathode-based AEMFCs reach a PPD of 1.80 W cm-2 along with an outstanding specific power of 13.87 W mg-1. Moreover, these AEMFCs can be operated under a 0.2 A cm-2 current density at 60 oC for over 300 h with a voltage decay rate of ~300 μv h-1.